Futures Explained in 200 Lines of Rust

This book aims to explain Futures in Rust using an example driven approach, exploring why they're designed the way they are, and how they work. We'll also take a look at some of the alternatives we have when dealing with concurrency in programming.

Going into the level of detail I do in this book is not needed to use futures or async/await in Rust. It's for the curious out there that want to know how it all works.

What this book covers

This book will try to explain everything you might wonder about up until the topic of different types of executors and runtimes. We'll just implement a very simple runtime in this book introducing some concepts but it's enough to get started.

Stjepan Glavina has made an excellent series of articles about async runtimes and executors.

The way you should go about it is to read this book first, then continue reading Stjepan's articles to learn more about runtimes and how they work, especially:

  1. Build your own block_on()
  2. Build your own executor

You should also check out the smol runtime as it's a real runtime made by the same author. It's well commented and made to be easy to learn from.

I've limited myself to a 200 line main example (hence the title) to limit the scope and introduce an example that can easily be explored further.

However, there is a lot to digest and it's not what I would call easy, but we'll take everything step by step so get a cup of tea and relax.

I hope you enjoy the ride.

This book is developed in the open, and contributions are welcome. You'll find the repository for the book itself here. The final example which you can clone, fork or copy can be found here. Any suggestions or improvements can be filed as a PR or in the issue tracker for the book.

As always, all kinds of feedback is welcome.

Reader exercises and further reading

In the last chapter I've taken the liberty to suggest some small exercises if you want to explore a little further.

This book is also the fourth book I have written about concurrent programming in Rust. If you like it, you might want to check out the others as well:

Credits and thanks

I'd like to take this chance to thank the people behind mio, tokio, async_std, futures, libc, crossbeam which underpins so much of the async ecosystem and and rarely gets enough praise in my eyes.

A special thanks to jonhoo who was kind enough to give me some valuable feedback on a very early draft of this book. He has not read the finished product, but a big thanks is definitely due.

Thanks to @ckaran for suggestions and contributions in chapter 2 and 3.


This book has been translated to Chinese by nkbai.